(a) Field of the Invention
The present invention relates to an electrostatic chuck of semiconductor fabrication equipment, and in particular, to a bipolar electrostatic chuck of which polarity is periodically alternated and a method for chucking wafers using the bipolar electrostatic chuck.
(b) Description of the Related Art
Typically, semiconductor devices are fabricated by repeatedly performing processes such as photolithography, etching, diffusion, ion implantation, metal deposition, chemical vapor deposition, etc. onto a wafer, and the wafers move between the processes in a carrier until being completed as semiconductor devices. The wafers carried in the carrier are moved to each process chamber by a transfer robot or an operator.
In order to fix the wafer at a working position, a mechanical means using vacuum pressure or an electrical means using electric characteristic is utilized. The electrostatic chucks are examples of the electrical means and have been disclosed in U.S. Pat. Nos. 5,572,398 and 5,933,314.
The electrostatic chuck can be classified into two types: a unipolar type and a bipolar type. The unipolar type electrostatic chuck is provided with a single electrode and forms an electric field by negative ions generated when the plasma stratum is formed so as to carry out chucking. Here, the wafer is isolated from the electrode by a dielectric material interposed between them.
In the meantime, the bipolar electrostatic chuck is provided with two electrodes isolated from each other and negative and positive voltages are supplied to the respective electrodes, resulting in chucking.
FIG. 1 is a schematic view illustrating a conventional bipolar type of electrostatic chuck.
As shown in FIG. 1, the electrostatic chuck includes an electrode part 110, a dielectric layer 120, and a power source 130 for supplying electric power to the electrode part 110. The electrode part 110 includes two electrodes 112 and 114 each having different pole so as to generate a static charge.
Not shown in the drawing, a lift that can move up and down can be installed so as to position the wafer at a predetermined height from the electrode part.
However, the conventional electrostatic chuck has a shortcoming in that the surface of the dielectric layer 120 of the electrostatic chuck is likely to be worn away due to abrasion while fixing the wafer (W) on the electrostatic chuck.
Also, since the conventional electrostatic chuck has a structure such that the positive and negative voltages are continuously applied to the respective positive and negative electrodes, the abrasion occurs differently according to the areas at which the electrodes are positioned as time passed, resulting in irregular abrasion distribution of the dielectric layer 120. Accordingly, the irregular abrasion causes a reduction of the life of the electrostatic chuck and the regularity of a thickness of a layer deposited during the high density plasma chemical vapor deposition (HDP CVD), making the electric charge unstable.